1. Summary / before you read / place in the series

• Regolith is a different material from soil on Earth: a poorly sorted powder made by meteorite impacts breaking bedrock, containing sharp agglutinates and with strong grain adhesion. On Apollo this dust affected suits and equipment in nine ways. [Ref. 1, 2]
• Water ice exists, but how much is usable is not known: in 2009 LCROSS estimated ice concentration at 5.6 ± 2.9% by mass from a single impact. NASA's 2025 material says water mining carries significant risk because resource knowledge is insufficient. [Ref. 4, 6]
• Oxygen extraction has advanced on the ground and in simulated lunar environments, but no demonstration on the Moon could be confirmed: carbothermal reduction and molten regolith electrolysis reached TRL 5-6 in simulated lunar environments. The lunar ISRU instrument PRIME-1 missed its goals because the lander ended up on its side. [Ref. 5, 6]

2. What regolith is: properties and the dust problem

Regolith is the layer of broken rock and powder covering bedrock. On the Moon, meteorite and micrometeorite impacts broke up bedrock over billions of years. According to NASA's McKay, about 90% of regolith is submillimeter particles (the part called lunar soil) and the rest ranges from rock fragments to boulders. The soil includes particles tens of nanometres in size. In addition there is "space weathering": melting and vapor condensation from impacts and implantation by solar wind and cosmic rays. [Ref. 1] Real samples are the 382 kg that Apollo brought back over six flights. [Ref. 3]Sourced

What stands out for engineering is that it is less well sorted than terrestrial soil, has strong grain adhesion, has many sharp-cornered agglutinates and an over-compacted density. [Ref. 1] Agglutinates are lumps in which impact-melted glass has bonded fine grains together (see glossary).Sourced

(1) What dust did on Apollo

NASA's Gaier examined records of the six landings and sorted dust effects into nine categories: vision obscuration, false instrument readings, coating and contamination, loss of traction, clogging of mechanisms, abrasion, thermal-control problems, seal failures, and inhalation and irritation. Simple measures stopped only some (such as loss of traction); serious effects such as clogging, abrasion and reduced heat rejection were not stopped. The report also says the severity of dust problems was consistently underestimated by ground tests. [Ref. 2] Suit components were approaching failure at the end of missions lasting 21 to 75 hours on the surface. [Ref. 2]Sourced

The effect on radiators shows up in numbers. The report says that only 11% dust coverage doubled solar absorptance, and that residual contamination depended mainly on particles smaller than 2 μm. [Ref. 2] This ties directly to the series articles on spacecraft thermal control and on thermal-control materials and radiative cooling.Sourced

3. Lunar resources: what and where

NASA's ISRU material lists the "commodities" it wants to produce on the Moon: oxygen, water and hydrogen, bulk and refined regolith, metals (aluminum, iron, titanium), silicon and ceramics, construction and manufacturing feedstock, fuels, plastics and hydrocarbons, and food feedstock. [Ref. 6] Broadly there are two families: extraction from regolith, which is everywhere (a powder of oxide minerals), and from water ice that may lie in the shadows of the polar regions.Sourced

(1) Water ice: the LCROSS observation and remaining uncertainty

To obtain direct evidence, the LCROSS mission on 9 October 2009 struck a spent rocket upper stage into the shadowed crater Cabeus near the south pole, and a second craft observed the ejected material with nine instruments. Near-infrared absorption and ultraviolet emission confirmed water vapor and ice; the maximum total of water vapor and ice observed was 155 ± 12 kg, and from the mass of excavated lunar soil that reached sunlight the ice concentration at the impact site was estimated at 5.6 ± 2.9% by mass. Light hydrocarbons, sulfur-bearing species and carbon dioxide were also found. [Ref. 4]Sourced

But this is an observation of one impact. NASA's 2025 material says the performance and viability of water extraction depend greatly on the form, concentration and distribution of the ice, which are currently unknown. It also says instruments that collect icy soil, heat it and measure water and volatiles still need to be developed to flight, and that no US instrument was funded for it. The water-prospecting rover VIPER is scheduled to arrive at the south pole in late 2027, carried by Blue Origin's second Blue Moon MK1 and equipped with a 1 m drill. [Ref. 6, 9] VIPER's arrival is still Not yet confirmed.SourcedNot yet confirmed

4. Extracting oxygen and metals

Lunar regolith is made of oxide minerals in which oxygen is bound to metals. Extracting oxygen needs reduction, pulling the bound oxygen away, and the heat and electricity for it would come from sunlight. NASA's material sorts ways of extracting oxygen from regolith by risk and performance into three: hydrogen reduction (low risk, low performance), carbothermal reduction (medium risk, medium performance) and molten regolith electrolysis (MRE) (high risk, high performance). [Ref. 6]Sourced

(1) Reading the numbers: oxygen yield from a real sample and how many tonnes of regolith are needed

A 1994 NASA paper reduced 10 g of Apollo 17 high-titanium basalt (sample 70035) with hydrogen at 900-1050 C and reported an oxygen yield of 2.93 to 4.61% of the sample weight. It was the first experimental demonstration of making oxygen from a lunar rock; water evolution was essentially complete in tens of minutes and yield depended little on temperature or pressure. Fe(2+) in ilmenite was fully reduced, while olivine and pyroxene were only slightly reduced. [Ref. 7] NASA's 2025 material, by contrast, reports for carbothermal reduction on a highland simulant a yield above 20% by weight, more than 20 g of oxygen per kWh of thermal energy and recovery of more than 99.7% of the carbon used (under simulated lunar vacuum and thermal conditions, five consecutive melts). [Ref. 6]Sourced

Converting these figures with a materials engineer's eye (Our calculation): to obtain one tonne of oxygen one needs about 25 tonnes of regolith at a 4% yield and about 5 tonnes at 20%. At 20 g/kWh of thermal energy, one tonne of oxygen needs at most about 50 MWh (thermal) (1,000,000 g / 20 g per kWh), an estimate for the best case that excludes equipment losses and the power for excavation and transport. The real constraints are therefore the quantity processed and the power to run it, not whether regolith is limitless.Our calculation

(2) Metals and other methods

Molten regolith electrolysis aims to obtain not only oxygen but also the metals iron, silicon and aluminum. According to NASA's material, Lunar Resources processed 25 kg of simulant over 36 hours (24 hours of electrolysis) and measured an oxygen rate matching theory; Blue Origin is developing MRE and purification reactors and equipment for solar cells and aluminum wire, with an integrated lunar-environment test planned for 2026 (company efforts and plans). [Ref. 6] In addition, vacuum vapor pyrolysis is at TRL 4, and all steps of hydrochloric reduction and molten-salt electrolysis of aluminum chloride are described as demonstrated. [Ref. 6] A meeting abstract also gives a proof of concept in which the FFC Cambridge (Metalysis) process electrochemically deoxidizes powdered regolith to give oxygen and metal-alloy powder. [Ref. 16] There is also a non-peer-reviewed preprint studying a configuration for extracting 10 tonnes of oxygen per year. [Ref. 18]SourcedNot yet confirmed

5. Stages of ISRU demonstration

ISRU has clear stages. (1) Ground analog tests: NASA tests ISRU hardware that extracts water and carbon dioxide on the volcanic terrain of Mauna Kea in Hawaii (described as usable also to validate technology for finding lunar ice). [Ref. 8] (2) Tests in a simulated lunar environment: in facilities simulating vacuum and temperature, carbothermal reduction ran five consecutive melts and MRE ran a single operation under near-lunar conditions. [Ref. 6] (3) Demonstration in actual space or on the Moon: this is the stage that is still sparse.Sourced

On the Moon, PRIME-1 (the drill TRIDENT and the mass spectrometer MSOLO aboard IM-2) touched down at Mons Mouton on 6 March 2025 at about 11:30, but because the lander was on its side, the PRIME-1 instruments were unable to accomplish their science, exploration and technology goals (NASA). [Ref. 5] TRIDENT was to retrieve samples down to 1 m and MSOLO to examine volatiles. NASA's 2025 material also says several important resource-exploration missions have "failed, cancelled or delayed." [Ref. 6] On Mars, MOXIE made oxygen from Martian carbon dioxide as the first ISRU demonstration on another planet (seven times between landing in February 2021 and the end of 2021). [Ref. 10]Sourced

The conclusions of NASA's 2025 material, as given (NASA's own view): (1) flight demonstrations of oxygen and metal extraction can proceed with reasonable risk; (2) extraction of lunar water and volatiles cannot proceed without significant risk because resource knowledge is lacking; (3) the performance and viability of water-mining methods depend greatly on the form, concentration and distribution of ice; (4) NASA has no technology-development work on processing icy regolith at present (work proceeds on company funds and investment). [Ref. 6]Sourced

6. Sintering and 3D printing as construction material

Consolidating regolith as it is into landing pads, roads, walls and foundations is the ISRU closest to a materials engineer. Landing pads are needed because a lander's engine plume blows the surface away, and NASA plans to carry an instrument (SCALPSS) on Blue Moon MK1 that images plume-surface interaction. [Ref. 9] Ways of consolidating include sintering (heating powder below its melting point so grains bond), melting, using binders and low-temperature chemical setting.Sourced

NASA's McKay says NASA programs have supported research on bricks by solar or microwave sintering, concrete, and microwave sintering and glazing. [Ref. 1] A 2022 Marshall Space Flight Center report studies sintering by microwave using the Moon's surface itself as a powder bed. Regolith has low thermal conductivity, but microwaves heat the whole volume and can bond the grains. The concept adds regolith layer by layer to build landing pads, blast shields and roads, and microwave systems, procedures and sintering conditions are being developed for a planned lunar demonstration. [Ref. 11]SourcedNot yet confirmed

Strength figures are in the reports. A 2016 NASA Kennedy report says sintering regolith needs heating above 1,000 C, gives compressive strengths of 14,000-28,000 psi (about 97-193 MPa) that depend heavily on porosity, and is brittle, and reports that bricks of the simulant JSC-1A made by a low-temperature method cured at 60 C reached 3,050 psi (about 21 MPa) (mean of two). [Ref. 13] Another 2023 NASA paper points out that many publications do not quantify how processing conditions affect strength and investigated, in vacuum, the factors that set quality using the highland simulant CSM-LHT-1G, which contains 30 wt% glass. [Ref. 12]SourcedOur calculation

7. A materials engineer's view, and what could not be confirmed

What could not be confirmed

• Any demonstration on the Moon of making oxygen or water from regolith or ice (none within what was checked)
• Reliable figures for the concentration, form and distribution of lunar water ice beyond LCROSS's single site
• The percentage chemical composition of regolith (this article states only figures confirmed in primary sources and gives no composition table)
• The durability of sintered bodies under lunar thermal cycling and any international standard for ISRU
• Reliable plant mass, power and operating time figures for companies' MRE and carbothermal systems (NASA's material gives only some performance figures)
• The current status of non-US ISRU instruments such as ESA's PROSPECT and ProSPA (NASA's material lists them but they were not individually checked)

Summary

Regolith is a material unlike terrestrial soil: poorly sorted, with sharp agglutinates and strongly adhesive grains, and on Apollo its dust affected equipment in nine ways. Water ice was confirmed by LCROSS but the usable amount is unknown. For oxygen extraction, carbothermal reduction and MRE reached TRL 5-6 in simulated lunar environments, and sintered bricks have reported compressive strengths of tens to over a hundred MPa on the ground. But no demonstration of making oxygen or water by ISRU on the Moon could be confirmed, and PRIME-1 missed its goals. ISRU is at the stage where concept and ground testing are advanced and lunar demonstration is yet to come.

8. How to read the yardsticks and standards

ISRU yardsticks still have few common standards and divide into technology readiness level (TRL), yield and energy, resource estimates and material strength. Checked on 17 October 2026.

The arrangement of the table is Our calculation (organization and conversion). No applicable ASTM standard was found.

Reading notes (for materials engineers)

• TRL depends on where it was tested: TRL 5-6 means testing in a simulated environment (ground vacuum and thermal facilities), not demonstration on the Moon. Do not read it as having operated on the Moon.
• Do not overlook "on simulant": many strengths, yields and powder behaviors are for simulant. Real regolith, especially at the south pole, has not yet been directly sampled.
• Separate company plans from NASA's assessment: the integrated MRE test (2026) and companies' lunar equipment are Not yet confirmed plans.

9. Glossary

10. References

1. NASA (NTRS) McKay D. "The Evolution and Development of the Lunar Regolith and Implications for Lunar Surface Operations and Construction" (2009: grain size, grain adhesion, agglutinates) — ntrs.nasa.gov/citations/20090022120
2. NASA (NTRS) Gaier J. R. "The Effects of Lunar Dust on EVA Systems During the Apollo Missions", NASA/TM-2005-213610 (2005: nine categories of effects) — ntrs.nasa.gov/citations/20050160460
3. NASA (Lunar Sample Laboratory) Lunar Samples (382 kg of Apollo samples) — curator.jsc.nasa.gov/lunar/
4. Science Colaprete A. et al. "Detection of Water in the LCROSS Ejecta Plume" (22 October 2010, DOI 10.1126/science.1186986; abstract) — doi.org/10.1126/science.1186986
5. NASA PRIME-1 Science (ISRU-related instruments on IM-2; unable to achieve goals because the lander was on its side) — science.nasa.gov/lunar-science/clps-deliveries/prime-1-im/
6. NASA (NTRS) Sanders G. and Kleinhenz J. "Progress Review of NASA Lunar ISRU Development: 2019 to 2025" (presentation at Luxembourg Space Resources Week, 19 May 2025) — ntrs.nasa.gov/citations/20250003730
7. NASA (NTRS) Gibson M. A. et al. "Reduction of lunar basalt 70035: Oxygen yield and reaction product analysis" (1994: oxygen yield 2.93-4.61%) — ntrs.nasa.gov/citations/19950028432
8. NASA In-Situ Resource Utilization (ISRU) (page on analog field testing at Mauna Kea, Hawaii) — www.nasa.gov/mission/in-situ-resource-utilization-isru/
9. NASA Moon Base Phases (VIPER: scheduled to arrive at the south pole in late 2027 aboard Blue Moon MK1) — www.nasa.gov/moonbase-phases/
10. Science Advances Hoffman J. A. et al. "Mars Oxygen ISRU Experiment (MOXIE)—Preparing for human Mars exploration" (2022, DOI 10.1126/sciadv.abp8636; PMC version) — pmc.ncbi.nlm.nih.gov/articles/PMC9432831/
11. NASA (NTRS) Effinger M. et al. "Scaleup of Microwave Powder Bed Fusion for Lunar Infrastructure Construction" (2022, Marshall Space Flight Center) — ntrs.nasa.gov/citations/20220005023
12. NASA (NTRS) Sibille L. et al. "Vacuum Sintering of Highland Simulant CSM-LHT-1G" (2023, Kennedy Space Center) — ntrs.nasa.gov/citations/20230008596
13. NASA (NTRS) Grossman K. et al. "Low Temperature Regolith Bricks for In-Situ Structural Material" (2016: sintered bricks 14,000-28,000 psi; low-temperature method 3,050 psi) — ntrs.nasa.gov/citations/20160007410
14. NASA (NTRS) Slabic A. et al. "Lunar Regolith Simulant User's Guide: Revision A" (1 October 2024) — ntrs.nasa.gov/citations/20240011783
15. NASA NPR 7123.1D "NASA Systems Engineering Processes and Requirements" (effective 5 July 2023; Appendix E Technology Readiness Levels) — nodis3.gsfc.nasa.gov/displayDir.cfm?t=NPR&c=7123&s=1D
16. ECS Meeting Abstracts Symes M. D. et al. "Proving the Viability of an Electrochemical Process for the Simultaneous Extraction of Oxygen and Production of Metal Alloys from Lunar Regolith" (2019, meeting abstract, DOI 10.1149/ma2019-02/57/2455) — doi.org/10.1149/ma2019-02/57/2455
17. NASA Commercial Lunar Payload Services (CLPS overview; updated 6 July 2026) — www.nasa.gov/commercial-lunar-payload-services/
18. EarthArXiv (preprint) Runyon K. et al. "A Systems-Level Approach to Extracting Oxygen from Lunar Regolith via Molten Regolith Electrolysis" (12 February 2025, DOI 10.31223/X5G438; not peer reviewed) — doi.org/10.31223/x5g438

11. Claim-to-source audit

Last updated: 17 October 2026. Sources are limited to primary materials (NASA technical reports, presentations and official pages, peer-reviewed papers and meeting abstracts). ISRU demonstration of oxygen or water on the Moon, water-ice concentration beyond LCROSS, the percentage chemical composition of regolith, durability of sintered bodies under lunar thermal cycling, international ISRU standards and ASTM standards could not be confirmed and are not stated. Many figures are from ground tests on simulant or in simulated lunar environments, and company plans are unconfirmed. All figures are conceptual diagrams or our own charts.